As we slog through the dog days of summer, I can't help but long for the shady cool of a grassy green roof. Enterprising city dwellers with limited square footage have long embraced the roof as an outdoor haven for grass or veggies, and even homes with plenty of space can reap some major benefits from growing a roof.

Rooftop garden anyone? These roofs are green in more ways than color; they're environmental rock stars, too. They insulate to keep your space cool in summer and warm in winter, which cuts down on energy use (and cost). They absorb rainfall to prevent landscape erosion and water waste, and they provide a healthy habitat for insects and birds.